1. Field of the Invention
This invention relates generally to injection molding. In particular, this invention relates to apparatus for moving intermediate mold members in so-called “stack mold” arrangements with movement of a movable platen.
2. Description of Related Art
It is known to arrange mold members in so-called “stack molds” to increase the number of articles that may be molded with a single cycle of operation of a molding machine. A “stack mold” is characterized as having two or more mold assemblies arranged so that intermediate mold members or mold assemblies are interposed between mold members mounted to, respectively, a stationary platen and a movable platen of a molding machine clamp unit. It is known to provide mechanisms for stack mold arrangements effective to “open” (separate) and “close” (engage) mating mold members of the two mold assemblies with movement of the movable platen. In certain of such known arrangements used in injection molding: a first mold assembly is arranged with a first mold member connected to a stationary platen (also referred to as a “fixed platen”); a second mold assembly is arranged with a third mold member connected to a movable platen; and a second mold member comprising the first mold assembly and a fourth mold member comprising the second mold assembly are supported so as to be interposed between and opposing, respectively, the first mold member and the third mold member and to be movable relative thereto. The interposed mating mold members are referred to herein collectively as “intermediate mold members” or “intermediate mating mold members”. Opening and closing of the mold assemblies is effected by moving the movable platen and the intermediate mold members to separate and engage, respectively, the first and second mating mold members and the third and fourth mating mold members. Motion of the movable platen is effected by at least one actuator comprising a clamp mechanism and motion of the movable platen is mechanically coupled to the intermediate mold members.
It is known to couple motion of the movable platen to the intermediate mold members using such devices as pivoting arms, mechanical drive mechanisms comprising at least one rack and drive pinion and mechanical drive mechanisms comprising helical gears and engaged nuts. In known drive mechanisms comprising helical gears, two helical gear portions with equal and opposed pitch are arranged on one helical gear segment and a region of each of the helical gear portions is received within an elongated engaging nut. One of the elongated engaging nuts is connected to the first mold member and the other elongated engaging nut is connected to the third mating mold member. A bearing support is interposed between the helical gear portions and connected to the interposed arrangement of mating mold members. Translation of the moveable platen is converted to rotation of the helical gear segment by the elongated engaging nut attached to the movable platen. Rotation of the helical gear segment is converted into translation of the helical gear segment by the elongated engaging nut connected to the stationary platen. Translation of the helical gear segment is coupled to the interposed arrangement of mating mold members by the bearing support.
In known helical gear mechanisms, the total length of the helical gear segment must be longer than the length of the desired separation of mating mold components of both mold assemblies to insure that the helical gear segment remains engaged with the elongated nuts when the mold assemblies are open. This length requirement may result in the length of the helical gear mechanism exceeding the separation between the opposed faces of the fixed platen and the movable platen when both mold assemblies are closed. In such circumstances, the helical gear segment can be arranged in the clamp unit to be outside the perimeter of the platens or the platens can be provided with clearance openings to accommodate the excess length of the helical gear mechanism. In the event the former is elected, substantial supports for the helical gear drive mechanism are required to resist deflection due to forces acting on the helical gear drive mechanism. In the event the latter is elected, placement of the clearance openings may be restricted by other components in the clamp unit. Hence, there is a need for an improved drive mechanism comprising helical gears and engaged nuts that is suitable for applications to accommodate large separations of mating mold components while permitting the helical gear drive mechanism to be located within the outline of the clamp unit platens without requiring clearance openings in those platens.